Rotary pump



Dec. 13, 1949 A. ZEITLIN 2,491,352

RRRRRRRR MP Filed Sept. 26, 1944 2 Sheets-Sheet 1 7 \b wgi //Zi INVENTOR. saw/v05? 22 W VW 4 TQF/VEY Dec. 13, 1949 A. ZEITLIN 2,491,352

v ROTARY PUMP Filed Sept. 26, 1944 2 Sheets-Sheet 2 i atented Dec. 13, 1949 UNITED STATES PATENT OFFICE ROTARY PUMP Alexander Zeltlin, New York, N. Y.

Application September 26, 1944, Serial No. 555,803

2 Claims. 1

This invention relates to rotary pumps or compressors of the sliding-vane type. In these pumps the rotor rotates about an axis within an eccentl'ic bore and carries the sliding. vanes which are at all times in engagement with the walls of the bore. The bore is so formed that its curvature causes the vanes to be alternately retracted and extended during each revolution of the rotor.

It has been found that certain sections of the bore are subjected togreater pressures than other sections and furthermore that in the sections of greatest pressure excessive wear occurs unevenly throughout the length of the section. This sets up vibrations and uneven discharge of the fluid in addition to causing excessive wear on the bore.

It is one of the principal objects of this invention to provide in a pump of the type described a bore which will not wear excessively, but which will wear evenly and thus not set up vibrations but will rather produce even, substantially ulsationless flow throughout the life of the pump.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

In the accompanying drawings,

Fig. 1 is a cross-section through a rotary pump of the sliding-vane type.

Fig. 2 is a diagrammatic representation of the bore illustrating the principles of this invention.

Fig. 3 is a graphic method of laying out the curvature of the bore in accordance with the principles of my invention.

Referring to Fig. 1 of the drawings there is shown a body ill of a rotary pump casing having a bore H which is formed of two diametrically opposed circular arcs l2 and 13 of difierent radii from a common center 0, connected by curves l4, I4 of special design to be more fully described hereinafter. The rotor 20 is mounted for rotation about axis and is of substantially the same radius as circular section l2 against which it bears. The rotor is provided with transverse diametric slots 22 within which operate vanes 23 of a length equal to the sum of the radii of circular sections l2 and 13. The vanes may be bore an expanding chamber for drawing fluid into the pump, while the vanes forced into the rotor constitute the discharge or pressure side by reason of a continuously decreasing chamber. In the case of an incompressible fluid such as a liquid, the inlet and outlet ports are co-extensive with the connecting curves l4, H, but in the case provided with bearing elements in the form of rockers 25 at their outer ends bearing on the of compressible fluids such as air or gas, the inlet and outlet ports may be of lesser length than the connecting curves.

It will be seen by reference to Fig. 1 that when i the vanes are in a position symmetrical with respect to the rotor, they project equally from each side of the rotor. In this position, and in this position only, the radius vector OD is equal to the radius vector OD. The radius vector is the straight line distance from the center of rota- I tion 0 to the wall of the bore. It will be seen that in the portion of the bore from point D to point A the radius vectors will be less than OD and in the portion of the bore from D to B the radius vectors will be greater than OD. The difference between OD and the radius vectors to other points of the bore may be indicated by r, and it will be apparent that the value of r is a function of the angle a measured from the base line DOD. If the total diflerence in length between the vane and the diameter of the rotor is indicated by p, then at points A and B the value of 1 will be The pressures which are exerted on the wall of the bore are not the same throughout the bore. This will become apparent from a study of the diagram in Fig. 2 wherein it is seen that during certain portions of a revolution of the rotor the vanes are being pushed into the rotor by the bore, thus exerting a strong reaction pressure on that portion of the bore, while in the opposite portions of the bore the vane is being extended from the rotor, thus exerting substantially little reaction pressure on that section of the bore. Also, during certain portions of the revolution of the rotor the vanes are exerting centrifugal force against certain portions of the bore, while in other portionsof the bore such force is not being exerted. Thus, for example assuming clockwise rotation of the rotor, in the portion of the bore BDA the curvature of the bore is such as to force the vanes into the rotor and thus the entire reaction pressure caused by acceleration of the vanes diametrically through the rotor is taken up by this section of the bore.

The sections of the bore A D' 13' however do not have to impart such acceleration to the vanes since the vanes are moving outwardly of the rotor. Furthermore, it will be noted that the center of gravity of each vane is at or below the base-line DOD at all times. Therefore, the portions of the bore D B and BD are subjected to the centrifugal force of the vanes. From this discussion it becomes apparent that there is one section of the bore, i. e. BD, which is subjected to both the acceleration force incident to imparting radial acceleration to the vanes and the centrifugal force of the vanes. It becomes apparent, therefore, that this section of the bore is critical because it is subjected to the maximum amount of pressure, and it is this section which heretofore developed unevenness which caused vibration, variations in discharge and rapid wear.

I have found that the remedy for the above conditions resides in causing the sum total of the pressures acting upon the bore to be substantially constant throughout the angular movement of the vanes and thereby unevenness of wear, with consequent rapid deterioration and vibration, is

avoided. In order to accomplish this result I so design the curvature of the bore that the sum total of the acceleration force of the vane radially of the rotor and the centrifugal force of the vanes will always be constant. In order to design such curve, the following consideration governs. By reference to Fig. 2 it will be seen that the centrifugal force will depend upon the distance of the center of gravity of the vane from the axis of rotation. This distance is equal to the value of T which is the amount by which the vane projection varies from its projection in the symmetrical position or base-line DOD in which position the center of gravity of the vane coincides with the axis of rotation 0. Further, we have seen that the value of r is a function of the angle of a radius vector drawn from the axis of rotation and measured from the base-line. Therefore it may be stated that the pressure due to centrifugal force is equal to r multiplied by a constant or PcI=K'T=K'F(U-) where F" stands for the second difierential of the function of.

The total pressure exerted on the section of the bore DB is therefore In order therefore to achieve the desirable results which I have set forth hereinbefore, the bore must be a curve in which PcI-I-Pac=a constant I. e.,

Fm) +[F"(a) a constant There are difierent methods by which a curve satisfying these conditions may be laid out. Thus, an equation may be devised in the form of a power series, or a logarithmic, exponential or trigonometric equation. Another method is the graphic method, and the principles of design by the graphic method are well-known. I have employed the graphic method herein as an example, as shown in Fig. 3, in laying out the portion DB of the bore. Fig. 3 represents a development of a curve wherein it will be seen that the sum of the For) and [-F'"(a)] at every point equals a constant. Similarly. the portion DA of the bore may be graphically designed, and since the bore is symmetrical, and in any case since the pump is reversible, the curvature of the section A D B will be the same as that of ADB.

The same formulas are used for arcs DA, D'A as for the arcs DB, DB' except that for the arcs DB and DB the value of r is added to the basic circle, whereas in arcs DA and DA' the value of r is deducted. Consequently, for each diameter, the value of T is added at one end and subtracted at the other. end. It is obvious that the length of the diameter thus remains constant in all positions, and since the vane has the length of this constant diameter it will engage the bore at both ends in all positions.

The following is a table of values of of gs:

relative to of angle on" worked out by the graphic design method, wherein an is the value of on between the base-line DOD and point B:

Graphically designed curve for which F(o:) +[-F"(a)] is substantially constant a in l-Fielplfl in of r=F (a) m 01' m of E a M121 51 52 s3 s4 55 5e 57 5s 59 60 e1 62 In accordance with the provisions of the patent statutes, I have herein described the principle and operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by other equivalent means. Also, while it is designed to use the various features and elements in the combination and relations described, some of these may be altered and others omitted without interfering with the more general results outlined, and the invention extends to such use.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. In a rotary pump or compressor having a body, a cylindrical rotor therein, said body having a bore eccentric with respect to the rotor, said rotor having radial slots and vanes slidable in said slots, the length of said vanes being greater than the diameter of the rotor, said vanes being adapted to be in contact with the bore in all positions, the eccentricity of the bore operating to expand and retract the vanes, certain portions of the bore being subjected to the centrifugal force due to the rotation of the vanes and to the acceleration force due to the radial acceleration of the vanes in the rotor, characterized by means for reducing wear of said portions, said means comprising the curvature of the bore in said portions so formed that substantially a constant for every position of the vanes on said portions, wherein 1' represents the distance between the center of rotation and the center of gravity of the vanes.

or represents the angle between a base line where the vanes project equally at opposite sides of the rotor and a radius vector drawn from the axis of rotation of the rotor to a point on said portions of the bore.

2. In a rotary pump or compressor having a body, a cylindrical rotor therein, said body having a bore eccentric with respect to the rotor, said rotor having radial slots and vanes slidable in said slots, the length of said vanes being greater than the diameter of the rotor, said vanes being adapted to be in contact with the bore in all positions, the eccentricity of the bore operating to expand and retract the vanes, certain portions of the bore being subjected to the centrifugal force due to the rotation of the vanes and to the acceleration force due to the radial acceleration of the vanes in the rotor, characterized by means for reducing wear of said portions, said means comprising the curvature of the bore in said portions so formed that F01) [-F"(a) ]=substantially a constant for every position of the vanes on said portions, wherein F represents function of.

or represents the angle between a base line where ALEXANDER ZEITLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,165,963 Curtis July 11, 1939 FOREIGN PATENTS Number Country Date 206,582 Great Britain Nov. 8, 1923 

